Thursday, October 9, 2014

Eyal Gal - 24GHz transverter

Coming back

For some time there was no new post from me, but here is the one that can be handy and interesting. I will try to bring your attention on this peace oh the "aluminum brick" called Eyal Gal transceiver. If you have one or if you are planing to buy one then you already have the G8CUB paper about it and the basics about building the 24GHz transverter.

Word of discouragement

Buying the Eyal Gal transceiver unit is just a half way to a working transverter, maybe not even a half way, let say 40%. I learn that on my unit, so be prepared to some extra sacrifices :-) and hiding the money from your wife :-) I will try not to repeat the good Roger Ray G8CUB article about this unit. Instead of that I will try to present my itinerary and the way how I made this thing to transmit.

First thing - shopping (Eyal Gal and ELCOM Ceragon)

I obtain my unit (two units) from the "24GHz microwave store" owned by a really BIG gentleman Ernie -HG5ED. It was a big gift from a big guy like he is. He knew that this is just a half of the story, so he included the local oscillator to drive this wild machine. Yes, you need the external local oscillator too, so start saving the money.... The local oscillator should work on the half frequency and what is required is the high side injection. As I choose the 70cm IF, the local oscillator should run on 12240MHz. This can be done using the various techniques, from the endless multipliers chain to the expensive low phase noise oscillators. My local oscillator is the CDFS-1295, ELCOM-Ceragon unit that can be found from time to time on the E-bay. More likely you will find the DFS1201 Ceragon unit that can operate from 11-12Ghz which is not good for this radio, we need the 1295 model running from 12-13Ghz. Whatever, you need the 10dBm @ 12240MHz signal. If you plan to use the Ceragon LO's then you need also the controller to run this unit. The controller can be found around the web together with the software for the PIC.

Second thing - more shoping (power supply)

OK, so you have the transceiver, the local oscillator and now you need the descent power supply for the Eyal Gal unit. As you already know, +8V, +12V and -12V are required for this unit. I start to make the first test with the old PC power supply where +/-12V is available and +8V was produced with a single 7808 voltage regulator. This can work, but if you plan to run your transverter portable on the car battery then the PC power supply is not a good option.The tricky part is obtaining -12V and 120mA. For that purpose I use the DC/DC converter (thanks to Ernie) where I have the +/-12V and 250mA output which should be more than enough for the negative supply. The positive 12V is obtained from the 12V rail external power supply or the battery.

Another tricky part may be the +8V where the consumption may reach over 1A in TX. This can be solved with the switching units. To make things simple, I use two 7808 regulators in parallel with the diode on the output. All the voltage regulators are fixed to the good heatsink.

Finally some soldering (IF switching unit)

So beside the L.O. delivering 10dbm you need a IF radio delivering -21dbm for the proper mixing. Of course, the attenuators are used. Take care, if you ran the IF radio with 2w of output you need 54dB of attenuation on 70cm which is not a trivial. If you used the relay for switching, it should be a good one, with the good isolation. Instead of that, I use the old fashioned switching with the PIN diodes. It is true that also on the RX side I have something about 5db of attenuation, I cure the problem with an extra MMIC amplifier in the RX side of IF switching unit. Of course, I was faced then with the extra gain and s-meter showing S-2. Then extra attenuator was introduced, which is not bad idea as the mmic see the nice 50ohms on input/output.

All those PINS (Eyal Gal transceiver)

The Eyal-Gal unit is a transceiver and not so much to switch around it. To make a story short, you need to key only PIN 1 and all the rest of the pins you can leave n/c.

But who want to know more:

Pin 1 is described as TX inhibit pin. It mean that you need to ground this pin when on RX and lift up when on TX. This will result better reception and less current consumption that leads to less heating of the Eyal-Gal at the end. So do not forget, PIN 1 to GND when on RX.

Pins 2 and 3 are n/c ( I love when the pins are n/c :-)

Pin 4 is 0V ( I left my n/c as I have enough ground through the housing )

Pin 5 is AGC To be correct, you can reduce the TX conversion gain by applying 0-5V dc. Leaving this port n/c :-) you will have the maximum gain (and the output power)

Pin 6 is a output power detector, where you can see by the DC voltage if you have the output power. I measure a bit more than 3V DC on that pin when on TX. Do not expect the voltage following the modulation! You will have constant (more or less) DC voltage as there is the 2xLO signal and both mixing products measured. This is why you need a filter on the TX output side !

Pin 7 is the RX AGC control. Well it works the same way like the pin 5, if n/c you will have the highest RX gain, if 0-5V dc applied you can reduce the RX gain.

Filtering (spending more money)

The output filter on the TX side is a MUST. Do not operate the transceiver without it because you may interfere with some cell tower links. You do not want to do that. You will have to look for a experience microwave guy help here or buy the tuned filter for the desired frequency.

Antenna switching

You probably heard the stories that antenna relay for the 24GHz operation should be a waveguide switch and nothing else... So why there are SMA coaxial relays on the market rated to operate up to 26.5GHz ? The E-bay is good source of such relays with a fair prices. More over the latching relay type can be purchased really cheap. Using the SMA relay will save you a troubles bending the waveguides, using the flexible waveguide and at the end the waveguide switch is really expensive. So the SMA coaxial relay is not only a cheaper but occupy less space and the box can be smaller, which also reduce the final cost of the transverter.

I did not measure the difference and the losses, but messing with the waveguide switch comparing to the SMA relay is not worth money and time.

First tests

Even the desk measurements on the instrumens were OK, the real test was performed listening the live signal on the band. Observe the frequency stability of the Eyal Gal transverter and the Mini beacon running some 4km away. The mini beacon will be explained in the next article. Note: none of the units were conected to the GPSDO reference.

Finally results :-)

At the end, what can be done with the 24GHz transverter described, so far I made the 236km QSO in a not so good conditions, means humidity 60%, temp 17 degC and pressure 1016hPa. The antenna used was a "footer" 32cm dish. The qso was a SSB with a solid copy both sides. Well, do not forget to switch the LSB on your radio when operating USB due to high side mixing. The drawback is that the tuning the frequency is opposite, but this should not be a problem for a experienced microwave operator.